JPA-如何使用表默认值生成主键？

Question

I have a table with primary key generation of TO_NUMBER(TO_CHAR(SYSDATE@!,'YYDDD')||LPAD(TO_CHAR(SEQ_REFID.NEXTVAL),11,'0'))

This has been given as default value for the table. When I insert through JDBC, I could leave the column as NULL, so the pk would be generated/defaulted and i'll get the key using getGeneratedKeys() method.

I require similar behavior using JPA. I'm a beginner in JPA. Pl help. Database used is Oracle 11g.

EDIT: The above mentioned value is not required to be table default. It can be applied from JPA layer if it is possible.

Other Entities depends on this Entity for the pk. PK must be passed over to all child tables.

Answer 1

Add the following annotation to the id field:

@Column(insertable = false)

This way, JPA will ignore the field when inserting new values and the database automatically generates the desired key.

However, you shouldn't use such a primary key. It effectively contains 2 different kinds of data in one column which should better be split into two seperate columns.

Make a simple id column with an ascending integer (and absolutely meaning other than " this is entry nr. x "). Then add an additional column with the current timestamp. This timestamp can have a default value and be protected against updates.

This is how it's supposed to be and not only simplifies your queries, but also improves the performance. You can query the table for entries of a specific hour, week and so on, or generate detailed statistics.

Don't try to put multiple information into one column. There's no advantage.

Answer 2

@Entity
public class Entity {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

}

Can also be

GenerationType.AUTO
GenerationType.SEQUENCE
GenerationType.TABLE

This reference describes the various strategies

Answer 3

Where did you get the idea that this default PK was a good idea?

If you want the creation time of the row, add a column to your table. Don't embed it in the PK like this.